1. Field of the Invention
This invention relates generally to detection of intrusion into electronic assemblies, and more particularly, to the detection of intrusion by mechanical means for the purpose of reading the data stored in a memory.
2. Description of the Related Art
As the value of computing systems increases and operating systems become more secure, physical attacks on computing systems to steal or modify assets become more likely. This invention describes a system and method for building a barrier around a computing system to prevent access to, or modification of the data and processing elements. In the event of an attack being detected, electronic circuitry in the computing system can detect the intrusion, erase all of the secret or critical data, and halt operation.
In many computer applications, it is desirable to protect the contents of the computer system from unlawful or unauthorized access. It is conventional practice to prevent reading of information electronically by providing certain encryption schemes wherein data is transmitted and received in an encrypted form and only authorized people who have the decryption key are able to read the data. A computer system, in this context, can be defined as all of the components being protected by this invention including, but not limited to, a microprocessor or microcomputer, its memory devices, its logic and control devices, input/output processing devices (including cryptographic processors, communication devices and processing elements), and all of the buses and interconnect wiring between the components. The invention prevents any access to the secret information contained or being processed in the protective device, as well as prevents observation or modification of the ongoing computing processes. In the event intrusion is detected, all processing is halted and all secret information is erased.
There are many different types of encryption schemes which are useful in protecting the sensitive data against being read by unauthorized persons. Encryption keys and other sensitive data are often stored in I/C (integrated circuit) memory components within the computer. By use of software, the stored information is generally adequately protected from unauthorized persons using keyboard entries to attempt memory interrogation.
However, an unauthorized person with the necessary skills and knowledge, and sufficient motivation can bypass software controls and attack the computer hardware directly. There are many attacks, some straight forward and well known, others more sophisticated, that allow direct interrogation of memory components and devices.
One scheme of protection against such attacks is to provide some type of detecting means which detect any attempted mechanical intrusion into the sensitive area of the computer. When such intrusion is detected an alarm is given and/or a signal is sent to circuitry, which erases the data, thereby preventing the compromise of the information which was stored in the computer memory components. Various schemes have been proposed which provide for some type of electronic or electrical grid surrounding the computer circuitry and, when this electrical grid is broken or breached, the requisite signal is generated.
These types of systems, however, have several drawbacks. One drawback is that many grids are susceptible to very careful mechanical manipulation that allows the computing system to be accessed without breaking or otherwise compromising the circuit. Still other more sophisticated attacks, through ionizing radiation (e.g. x-rays) affect volatile memory devices such that an erasure command is not effective, thereby allowing the electrical wrapping to be circumvented.
The present invention overcomes these defects by providing a flexible mesh assembly structure that includes uniquely designed resistive structures that detect intrusion and other physical damage. Further, the resistive structures make the flexible mesh assembly optically opaque and may obscure x-ray and other ionizing radiation intrusion.
It is, therefore, an object of the present invention to provide a structure and method for a tamper respondent electronic circuit enclosure having an integrated circuit structure, a mesh structure surrounding the integrated circuit structure, and a sealed enclosure surrounding the mesh structure. The mesh structure includes a layer of flexible dielectric having a first side and a second side, a screen-printed pattern of flexible electrically conductive first circuit lines forming a first resistor network on the first side, and a photolithographically-formed pattern of flexible electrically conductive second circuit lines forming a second resistor network on the second side. When viewed from the side, the first circuit lines appear interleaved with the second circuit lines. The first circuit lines comprise conductive ink lines and the second lines comprise metal lines. The electronic circuit enclosure can also include an electrical connection between the first circuit lines and the second circuit lines, and a pressure sensitive adhesive adapted to connect the mesh structure to the integrated circuit structure. The first circuit lines may have a different width than the second circuit lines.
The invention can also include a method of manufacturing a tamper respondent electronic circuit article which includes screen printing a pattern of flexible electrically conductive first circuit lines forming a first resistor network on a first side of a flexible dielectric and photolithographically forming a pattern of flexible electrically conductive second circuit lines which form a second resistor network on a second side of the flexible dielectric.